This invention relates to abrading tools generally and, more specifically, to the construction of honing stones, grinding wheels, abrasive cut-off wheels and the like, with particular reference to the configuration, composition and arrangement of abrasive elements therein. The typical conventional abrasive tool comprises a body of matrix material that is shaped according to the particular abrading operation that is to be performed, with abrasive grains or grit interspersed through and held by the matrix material to provide a wearable abrasive face on at least one side of the body, Conventional granular abrasives may be either natural or synthetic materials and include silicon carbide, aluminum oxide (both in natural and synthetic forms), boron carbide, garnet, silica and diamond, the latter being quite expensive and used primarily in chip or dust form for special applications.
With grains of such material mixed throughout a relatively hard, wearable matrix material, the working face of the stone or wheel comprises a large number of grits embedded in the matrix and partially exposed for abrading contact with a workpiece. During rubbing contact with the work, each exposed particle abrades the work and is itself consumed, either by gradual wearing, by fracturing to expose new abrading surfaces, or by breaking loose from the matrix material and being lost from the tool when the amount of the particle embedded in or bonded to the matrix becomes insufficient to hold the particle, such breaking loose being known as "shelling". At the same time, the surface portion of the matrix material wears away, thus progressively exposing new layers of grit for contact with the work. It will be evident, of course, that the wearing and abrading characteristics of a particular stone or wheel will depend upon the type and size of the grains, the nature of the matrix material, and the pressure with which the tool is pressed against the work, and all of these factors must be considered in the selection of a tool for a given job.
Because of variations in the number of exposed grits at any time, the variable retention of the grit in the matrix material, and the variable abrasive nature of the individual grits, there is a general lack of consistency and, thus, predictability with respect to the precise abrasive performance of a tool at any given instant during an abrading process. In addition, the wear rate often is relatively rapid because of shelling of grits before they have exhausted their abrasive capability, and heat generated during abrading is largely confined to the working surface of the tool, because of the insulating characteristics of the matrix material, often requiring continuous flushing of the work area with coolant during heavy-duty abrading operations to reduce heating of the work and the tool. Despite these and other shortcomings, grit-type abrading tools have been the most practical available tools and are widely used.